JPH107909A - Silicone rubber composition for covering of electric wire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a silicone rubber compsn. for covering of an electric wire which possesses good electrical insulation resistance and excellent core wire adhesion resistance by mixing a particular diorganopolysilioxane crude rubber, a finely divided silica, a zinc compd., and a particular benzoyl peroxide together. SOLUTION: This silicone rubber compsn. for covering of an electric wire comprises: (A) 100 pts.wt. diorganopolysiloxane raw rubber represented by average compsn. formula, Ra SiO(4-a)/2 (wherein R represents a substd. or unsubstd. monovalent hydrocarbon group and (a) is an no. of 1.95 to 2.05); (B) 10 to 150 pts.wt. finely divided silica; (C) 0.01 to 20 pts.wt. zinc compd.; and (D) 0.1 to 10 pts.wt. methyl-substd. benzoyl peroxide. The component (C) is pref. a zinc oxide powder having an average particle diameter of not more than 50μm, and is more pref. zinc stearate. The component (D) is pref. o- methylbenzoyl peroxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicone rubber composition for covering electric wires, and more particularly, to a method of coating an electric conductor (eg, copper wire, tin-plated copper wire, etc.) with silicone rubber, which has a high electric insulation resistance. Also, the present invention relates to a silicone rubber composition for covering electric wires, which can prevent adhesion or adhesion (hereinafter referred to as core wire adhesion) between an electric conductor and silicone rubber.

[0002]

2. Description of the Related Art Silicone rubber is used as an electric wire covering material because of its excellent heat resistance, cold resistance and weather resistance and excellent electrical insulation resistance. However, this kind of silicone rubber has a weak point that its mechanical strength is lower than that of general organic rubber. For this reason, in the silicone rubber-coated electric wire, it is required that a braid such as a glass braid be provided on the silicone rubber insulating layer to reinforce it. In addition, various varnishes are used as a convergence material to converge the braid. However, when the varnish is cured by heat treatment, core wire adhesion easily occurs between the silicone rubber insulating layer and the electric conductor. . A phenomenon similar to this also occurs when a silicone rubber-coated electric wire is subjected to secondary heat treatment in order to improve electrical characteristics, and is a very important problem in processing. That is, the silicone rubber-coated electric wire has a problem in that, when the terminal processing such as soldering is performed, the core wire adheres, and a problem that the silicone rubber remains on the electric conductor occurs, and the terminal processing may not be performed. Was. Conventionally, as a method for preventing such core wire adhesion, there is known a method in which a composition obtained by mixing a fatty acid or a fatty acid metal salt and zinc oxide powder with a silicone rubber composition is heated and cured using 2,4-benzoyl peroxide as a curing agent. (See Japanese Patent Publication No. Sho 62-26124). However, in this method, a large amount of a fatty acid or a fatty acid metal salt and zinc oxide must be blended in order to prevent core wire adhesion, and as a result, there is a disadvantage that electric characteristics represented by electric insulation resistance are reduced. As a result, the silicone rubber composition for covering electric wires was not always sufficiently satisfactory.

[0003]

SUMMARY OF THE INVENTION The present inventors have conducted intensive studies to solve the above problems, and found that a silicone rubber composition containing a zinc compound was cured by heating using a special organic peroxide as a curing agent. The present inventors have found that a silicone rubber composition having good core insulation and good electrical insulation resistance and excellent core adhesion can be obtained, and have reached the present invention. That is, an object of the present invention is to provide a silicone rubber composition having good electric insulation resistance and excellent core wire adhesion resistance.

[0004]

The object of the present invention is to provide (A) an average composition formula R _a SiO _{(4-a) / 2} (where R is a substituted or unsubstituted monovalent hydrocarbon group, and a is 1.95) 100 parts by weight of a diorganopolysiloxane raw rubber represented by the following formula: (B) 10 to 150 parts by weight of finely divided silica, (C) 0.01 to 20 parts by weight of a zinc compound, and (D) ) Methyl group-substituted benzoyl peroxide in an amount of 0.1 to 10 parts by weight.

[0005]

The present invention will be described in detail. The diorganopolysiloxane raw rubber (A) used in the present invention is a main component of the composition of the present invention. The component (A), represented by the average compositional formula _{R a SiO (4-a)} / 2. R in the formula is an alkyl group such as a methyl group, an ethyl group, or a propyl group; an alkenyl group such as a vinyl group, an allyl group, a butynyl group, or a hexenyl group; an aryl group such as a phenyl group;
3-trifluoropropyl group, 2-phenylethyl group,
Monovalent hydrocarbons exemplified by substituted hydrocarbon groups such as a 2-cyanoethyl group are exemplified. The molecular structure of this component is a linear or partially branched linear diorganopolysiloxane. Examples of the siloxane unit constituting the diorganopolysiloxane include dimethylsiloxane, methylvinylsiloxane, methylphenylsiloxane, diphenylsiloxane, phenylvinylsiloxane, and methyl 3,3,3-trifluoropropylsiloxane. The degree of polymerization of this component can be used within the range referred to in the art as organopolysiloxane raw rubber, and usually has a viscosity at 25 ° C. of 10 ⁷ centistokes or more, and an average molecular weight of 25 × 10 ⁴ or more. Things are used. The diorganopolysiloxane may be a homopolymer or a copolymer or a mixture thereof. The terminal of the molecular chain includes a hydroxy group, an alkoxy group, a trimethylsilyl group, a dimethylvinylsilyl group, a methyldiphenylsilyl group, a methylphenylvinylsilyl group, and a dimethyl 3,3,3-trifluoropropylsilyl group.

The finely powdered silica (B) used in the present invention is an essential component for imparting excellent mechanical strength to the silicone rubber obtained by curing the composition of the present invention. . Examples of such finely powdered silica include dry-process silica such as fumed silica, wet-process silica such as precipitated silica, and organic silica such as organosilane, organosilazane, organopolysiloxane, and diorganocyclopolysiloxane. Fine powdered silica hydrophobized with a silicon compound may be used. This component has a particle size of 50 μm or less, and preferably has a specific surface area of 50 m ² / g or more, and more preferably 100 m ² / g or more. If the amount of this component is too small, the mechanical strength after curing becomes insufficient, and if it is too large, it becomes difficult to mix it with the component (A).
It is in the range of 0 to 150 parts by weight.

The zinc compound (C) used in the present invention is a component essential for preventing core wire adhesion.
Ingredients include powders of inorganic zinc compounds such as zinc oxide, zinc carbonate, zinc hydroxide, zinc sulfide, zinc selenide, and fatty acids such as zinc stearate, zinc palmitate, zinc caprylate, zinc laurate, and zinc oleate. Zinc compounds are exemplified. Among these, zinc oxide powder, zinc carbonate powder, and zinc stearate are preferred. Here, when zinc oxide powder or zinc carbonate powder is used, the average particle diameter is preferably 50 μm or less. The compounding amount of this component is in the range of 0.01 to 20 parts by weight, preferably 0.1 to 10 parts by weight, per 100 parts by weight of component (A). If the amount is less than 0.01 part by weight, the core wire adhesion after curing of the composition of the present invention cannot be prevented, and even if an amount exceeding 20 parts by weight is added, the effect does not change. Because it has a negative effect on

[0008] The methyl-substituted benzoyl peroxide of the component (D) used in the present invention is a curing agent for curing the composition of the present invention. This has a unique function of preventing core wire adhesion without lowering the electrical insulation resistance when used in combination with the zinc compound (C).
Examples of the methyl-substituted benzoyl peroxide of the component (D) include monomethyl benzoyl peroxide, dimethyl benzoyl peroxide, and trimethyl benzoyl peroxide. Specifically, o-methyl benzoyl peroxide, m-methyl benzoyl peroxide, p-methylbenzoyl peroxide, 2,3-dimethylbenzoyl peroxide, 2,4-dimethylbenzoyl peroxide, 2,6-dimethylbenzoyl peroxide, 2,3,4-trimethylbenzoyl peroxide, 2,4,6 -Trimethylbenzoyl peroxide and the like. In particular, o-methylbenzoyl peroxide, m-methylbenzoyl peroxide,
p-Methylbenzoyl peroxide and 2,6-dimethylbenzoyl peroxide are preferred in terms of price and performance. Incidentally, the methyl-substituted benzoyl peroxide of the component (D) is known (see Japanese Patent Publication No. 3-54138) and is commercially available. The amount of this component is (A) component 10
It is in the range of 0.1 to 10 parts by weight with respect to 0 parts by weight. When the amount is less than 0.1 part by weight, the physical properties of the cured silicone rubber of the composition of the present invention are reduced. When the amount exceeds 10 parts by weight, the silicone rubber becomes too hard, which is economically disadvantageous. It is.

The composition of the present invention is a silicone rubber composition comprising the above-mentioned components (A) to (D). In addition to these components, a silanol group at both ends may be used as a crepe hardening inhibitor if necessary. Blocked diorganopolysiloxane, organosilane, organosilazane and the like may be added. Also, various additives conventionally known to be used in silicone rubber compositions, for example, diatomaceous earth, quartz powder, semi-reinforcing fillers such as calcium carbonate and titanium oxide, carbon black Addition of a pigment such as a red iron oxide, a rare earth oxide, a heat resistance improver such as cerium silanolate, a cerium fatty acid salt or the like may be added as long as the object of the present invention is not impaired.

The composition of the present invention can be easily produced by uniformly mixing the above-mentioned components (A) to (D). In this case, after the components (A) and (B) are uniformly mixed in advance in a kneading device such as a kneader mixer or a Banbury mixer, the kneading means such as a two-roll mill is used, and the components (C) and (D) are mixed. )
In general, the components are mixed to form a silicone rubber composition comprising the components (A) to (D).

In order to produce a silicone rubber-coated electric wire by applying the composition of the present invention to an electric wire, the composition of the present invention is introduced into a well-known extruder for coating a wire and coated on an electric conductor. A general method is to introduce an electric conductor coated with the composition of the present invention into a hot air heating furnace and heat it for several seconds to several minutes at a temperature of 200 to 500 ° C.

The composition of the present invention as described above becomes a silicone rubber which has good electric insulation resistance after curing and does not cause core wire adhesion. Therefore, it is considered to be extremely useful as a silicone rubber composition for covering electric wires by utilizing such characteristics.

[0013]

Next, the present invention will be described with reference to examples and comparative examples. In Examples, “parts” means “parts by weight”. In the examples, the electrical insulation resistance and the core wire adhesion were measured according to the following methods. ○ Electrical insulation resistance JIS-C-3
004. ○ Core wire adhesion Silicone rubber coated wire is heated at 180 ° C, 20
Secondary heat treatment was performed by heating at 0 ° C. for 4 hours. The silicone rubber layer of the silicone rubber-coated electric wire after the secondary heat treatment was peeled off with a wire stripper, and the adhesion of the silicone rubber to the core wire was measured. ○ No core wire adhesion (no silicone rubber residue on core wire) △ Slightly core wire adhesion (a small amount of silicone rubber residue is found on core wire) × Core wire adhesion (silicone rubber adheres on core wire I couldn't pull it off)

[0014]

EXAMPLE 1 100 parts of an organopolysiloxane rubber having a dimethylvinylsiloxy group at both ends and having 99.6 mol% of dimethylsiloxane units and 0.4 mol% of methylvinylsiloxane units (polymerization degree: 5000), and having a viscosity of 60 at 25 ° C. 8 parts of dimethylpolysiloxane having a silanol group at both ends, which is a centistoke, and specific surface area of 200 m ²
/ G of dry-processed silica of 40 g / g into a kneader-mixer and kneaded under heating until uniform, then, after cooling, 0.5 part of cerium oxide and 10 parts of diatomaceous earth were added to give base compound 1 Obtained. Next, 100 parts of the base compound were mixed with zinc oxide powder, zinc stearate, and o-methylbenzoyl peroxide in amounts shown in Table 2 on two rolls to prepare a silicone rubber composition.
This composition was introduced into an extruder and placed on a core wire (tin-plated soft copper wire) having an outer diameter of 1.0 φmm (20 wires / 0.18 mm).
And the core wire was covered. Next, it was shaped into an electric wire by passing through a hot air heating furnace at 400 ° C. for 18 seconds. The insulation resistance value of the silicone rubber-coated electric wire thus obtained was measured according to the method specified in JIS-C-3004. Further, after these silicone rubber-coated electric wires were subjected to secondary heat treatment in a heating furnace at a predetermined temperature and for a predetermined time, the silicone rubber was peeled off with a wire stripper, and the adhesion to the core wire was measured.

[Table 1]

[0015]

Example 2 100 parts of an organopolysiloxane raw rubber having a dimethylvinylsiloxy group at both ends capped with 99.6 mol% of dimethylsiloxane units and 0.4 mol% of methylvinylsiloxane units (degree of polymerization 5000), having a viscosity of 60 at 25 ° C. 4 parts of dimethylpolysiloxane having capped end silanol groups and 40 parts of dry-processed silica having a specific surface area of 250 m ² / g treated with dimethyldichlorosilane were charged into a kneader mixer until the mixture became uniform under heating. After kneading, the mixture was cooled and then 0.5 part of cerium oxide and 10 parts of quartz powder were added to obtain a base compound 2. Next, zinc oxide powder, zinc stearate, p-
Methylbenzoyl peroxide was added and blended in the amounts shown in Table 2 to prepare a silicone rubber composition. This composition was introduced into an extruder, and the outer diameter was 1.0 φmm (20 pieces / 0.18 mm).
Was extruded at a thickness of 0.5 mm onto a core wire (tin-plated soft copper wire) to cover the core wire. Next, it was shaped into an electric wire by passing through a hot air heating furnace at 400 ° C. for 18 seconds. The insulation resistance value of the silicone rubber-coated electric wire thus obtained was measured according to the method specified in JIS-C-3004. Further, after these silicone rubber-coated electric wires were subjected to secondary heat treatment in a heating furnace at a predetermined temperature and for a predetermined time, the silicone rubber was peeled off with a wire stripper, and the adhesion to the core wire was measured.

[Table 2]

[0016]

The silicone rubber composition for covering electric wires according to the present invention comprises the above-mentioned components (A) to (D).
Since it contains the zinc compound (C) and the methyl-substituted benzoyl peroxide of the component (D), it has excellent insulation resistance and excellent core wire adhesion resistance.

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Claims (4)

[Claims] (A) an average compositional formula: R _a SiO _{(4-a) / 2} (wherein R is a substituted or unsubstituted monovalent hydrocarbon group, and a is 1.95 to 2.05) 100 parts by weight of a diorganopolysiloxane raw rubber, (B) 10 to 150 parts by weight of finely divided silica, (C) 0.01 to 20 parts by weight of a zinc compound, and (D) methyl-substituted benzoyl. A silicone rubber composition for covering electric wires, comprising 0.1 to 10 parts by weight of peroxide. 2. The silicone rubber composition according to claim 1, wherein the component (C) is a zinc oxide powder having an average particle size of 50 μm or less. 3. The silicone rubber composition for covering electric wires according to claim 1, wherein the component (C) is zinc stearate. 4. The silicone rubber composition according to claim 1, wherein the component (D) is o-methylbenzoyl peroxide.